Increases in the complexity of aerospace structures have made NDI/NDE, which terms are used interchangeably herein, more and more difficult to apply successfully and cost-effectively. Often, a region of a particular structure requires inspection, but is inaccessible for the application of conventional NDE methods. In some cases such inspection requirements of regions with limited access have prompted part removal to improve access, or expensive redesigns altogether. Conventional tools include extenders and manipulation arms to reach into limited access areas and to aid probe placement on or near limited access areas of aircraft. Such areas may be cavities or obstructed areas, and include, for example, the interior of aircraft wings.
When in operation, certain sensors for detection of defects in a surface are preferably seated on the surface, or at least require maintaining no more than a maximum clearance from the surface. When a sensor, for example an eddy current sensor, is not completely seated on the surface, which may be referred to as “lift-off,” the result may be a reduced sensitivity to small cracks.
A sensor may be applied to a surface that is not completely flat and require movement of the probe along the surface, or may be mounted to a rotating end of a probe for NDE in limited access areas. Either case may result in lift-off. For the rotating application, if the probe end is not exactly perpendicular to the surface to be inspected, the rotating path of the sensor will be eccentric; although the sensor may be flush with the surface at one point along the path, at an opposite point on the path there will be lift-off. Accordingly, apparatus is needed that addresses lift-off to provide adequate sensitivity for detection of defects over the full range of motion of the sensor.